staging: mt7621-mmc: Add blank line after declaration

Correct the following warning from checkpatch.pl:

WARNING: Missing a blank line after declarations
+		struct msdc_host *host = mmc_priv(mmc);
+		msdc_pm(state, (void *)host);

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@protonmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>